Internal combustion engines are used in a wide variety of applications. As a result of the internal combustion process, and the need for fuels to perform that process, such engines necessarily generate emissions having a variety of carbon-based and other substances. Increasingly, it is desired that internal combustion engines operate in a manner such that at least one or more components of these emissions be reduced or eliminated.
Further, small engine manufacturers are subject to both exhaust and evaporative emissions regulations by the Environmental Protection Agency (EPA) and California Air Resource Board (CARB) commencing with engines produced for the 2006 model year. The emissions limitations set by these agencies will become more stringent with each successive year and are expected to plateau in the year 2009. Hydrocarbon molecule concentration is the primary component measured by the EPA and CARB.
A major source of hydrocarbon emissions from internal combustion engines is evaporated fuel emanating from plastic fuel tanks, which are typically made from high density polyethylene (HDPE), polypropylene, polyamide (PA) or other low cost materials, as well as fuel tank caps. An additional source of evaporative emissions is evaporated fuel emanating from carburetors.
One approach being adopted by the small engine industry to reduce such evaporative emissions is to employ the use of a carbon canister (CC) as a temporary repository of fuel vapors produced by the fuel tank, the carburetor fuel bowl or a combination of the two when the engine is not functioning. At some time upon start-up of the engine, the CC is purged of the stored vapor. This type of control system is commonly referred to as an “open system design.”
There are typically two types of control valves associated with a CC. The first type of valve is known as a roll-over valve (ROV). Most commonly, a ROV couples the CC to the fuel tank, and functions to allow vapor to vent only from the fuel tank. The ROV must prevent liquid from entering the CC or it will be rendered useless. In some systems, there is an additional ROV by which the CC is attached to the carburetor fuel bowl vent. The second type of valve is known as a purge valve (PV), and functions to control vapor flow from the CC into the main induction line of the carburetor to the engine. The PV is controlled by engine manifold operation, venturi vacuum operation, or a combination of the two processes.
Although the open system design does provide some control over evaporative emissions, such a system has several disadvantages. First, the CC can be damaged from excessive engine vibration. Second, the CC can be rendered useless if liquid fuel enters the carbon chamber. Third, it can be difficult to locate the components of an open system design such that the components are not damaged from interaction or friction with other engine components. Fourth, when the system contains only one ROV, hydrocarbon emission from the carburetor is not accounted for and can potentially be released, thereby resulting in undesirably high emissions (such as could result in an emission level test failure). The addition of a second ROV to the carburetor can potentially help to reduce this problem but can be costly.
Therefore, it would be advantageous if an improved system (or systems) could be developed for reducing hydrocarbon leakage or evaporation of fuel (or potentially other emissions) into the surrounding environment from internal combustion engines including, for example, small engines. In at least some embodiments, it would be advantageous if such an improved system was capable of reducing the amount of fuel vapor escaping from several engine components including, for example, the carburetor, the carburetor fuel supply hose, vacuum hoses, the fuel tank and/or the fuel tank filler cap.